1. Field of the Invention
The invention relates to smelting furnace venturi gas scrubbers of the so-called Warkaus-type for use in electric smelting furnaces.
2. Description of the Prior Art
Smelting furnaces used in metallurgical processes give off metallurgical dusts in the flue gases and these dusts must be removed because they are environmental pollutants. They are usually removed by a wet scrubbing system, usually by a number of stages of venturi gas scrubbers. In smelting furnace venturi gas scrubbers, the velocity of the gas to be scrubbed must be high to prevent back-flow and the deleterious effects thereof with respect to clogging. Warkaus-type venturi scrubbers operate on the principle that the energy which is necessary to impart the velocity to the gases to scrub them is supplied by means of the scrubbing fluid. The scrubbing fluid is usually water and in Warkaus-type scrubbers is supplied to the system at relatively high pressure; the pressure may, for instance, be around 25 Kg/cm.sup.2 but usually not less than 5 Kg/cm.sup.2 for scrubbing gases from electric smelting furnaces. This is in contra-distinction to the venturi scrubbers in which the high gas velocity is achieved using fans or other similar devices.
A smelting furnace Warkaus venturi scrubber consists usually of a number of venturi tubes which operate in series. The separation of the coarser particles in the gases takes place in the first tube while the separation of the finer particles takes place in subsequent tubes. The nozzle through which the scrubbing fluid is supplied is arranged centrally in the narrowest part of the venturi tube in the stream of the gases and the feed pipe through which the scrubbing fluid is conducted to the nozzle is laterally introduced into the tube through its wall. Positioning the nozzle feed pipe in the first venturi tube in the stream of hot unscrubbed gases, which is required to impart the necessary velocity to the gases, results in condensation and deposits on the fluid feed pipe leading to eventual clogging of the system. Surrounding the fluid feed pipe with a steel pipe together with interfacial insulation between the two pipes has been tried. The outer pipe, which terminates above the level of the nozzle, will tend to be at a temperature which is higher than the condensation temperature and this arrangement has improved the conditions to a certain degree. But in those cases where the gas scrubbing plant is operated at reduced load, conditions may occur which cause the scrubbing fluid from the nozzles to have a pulsating motion so that the fluid tends to strike back and moisten the exposed surface of the outer pipe. This will again cause condensation and deposits, leading to eventual clogging of the system. Thus, a conventional Warkaus arrangement in which the scrubbing fluid imparts a high velocity to the gases, even with the aforementioned improvement, does not yield entirely satisfactory results when used as a first stage to scrub gases from a smelting furnace. The Warkaus arrangement is more satisfactory, however, for applications in which there is not a transistion from a dry zone to a wet zone, as for example in subsequent stages of scrubbers for smelting furnaces or in completely wet or completely dry applications.